The present invention relates to a reflection plate for a backlight unit in a liquid crystal display device, and more particularly, to a reflection plate for a backlight unit in a liquid crystal display device, which is made of a thermoplastic thermal conductive resin composition having a thermal conductivity of at least 0.35 W/mK, thereby effectively solving the thermal problem of the backlight unit, and having excellent properties such as shock resistance, heat resistance, mechanical strength, and the like, as well as having excellent reflectivity, thereby improving the durability of the liquid crystal display device. Furthermore, the present invention relates to a backlight unit of a liquid crystal display device, comprising a reflection plate positioned at a lower portion of a lamp of the backlight unit for reflecting the light coming out of the lamp, a supporting rod for the lamp, and a lower plate functioning as a heat sink, wherein the reflection plate and the lower plate are made of the same material, thereby effectively solving the thermal problem of the backlight unit, and simplifying the manufacturing process.